Glass products has hitherto been colored by incorporating metal ions such as iron ion, chromium ion and cobalt ion as a coloring agent in raw materials of glass. However, collected colored cullet does not become colorless by heating and fusing due to the above-mentioned metal ions. A demand for recycling glass bottles has been increasing in recent years. However, the other colored bottles than brown bottles are not suitable for recycling because their colors remain even after fusion. Such bottles are disposed mainly as waste products.
In order to make the heated and fused products colorless, Japanese Laid-open Patent Publication No. 320742/1989 proposed a method of forming a glass gel coating film at heating temperatures of 500.degree. C. or lower by a sol-gel method through hydrolysis and polycondensation of metal alkoxides using coating compositions containing the metal alkoxides, water, acids, alcohols, and organic pigments and dyes as coloring agents. However, the glass gel coating film obtained at the heating temperatures of 500.degree. C. or lower by the sol-gel method has a lot of pores and tends to become porous. As a result, no dense film is obtained, and the obtained film causes the problems that the film is not good in water resistance and the dyes are eluted owing to invasions of water, chemicals, etc. into the pores of the film surface.
In order to solve these problems, Japanese Laid-open Patent Publication No. 178623/1993 proposed a method of forming a glass gel coating film wherein heating is carried out at the temperature of 500.degree. C. lower by the sol-gel method using coating compositions containing pigment particles having particle diameters being larger than those of pores of the glass gel coating film.
However, the method has the following defects. Adjustment of the particle diameters to obtain the pigment particles having the particle diameters being larger than that of the pores of the glass gel coating film is troublesome. Further, the compositions cannot provide the products having desired sufficient water resistance.
As mentioned above, the glass gel coating films having photo absorptivity have hitherto been formed by the sol-gel method. In this process, however, heating temperatures of the films were controlled at a low temperature in terms of heat resistance of coloring agents. Consequently, the obtained glass gel coating films were porous and caused the problems with water resistance, boiling water resistance, alkali resistance, weather resistance, etc. as mentioned above.
An object of the present invention is to provide colored coating compositions which can easily form a colored glass gel coating film which is excellent in water resistance, boiling water resistance, alkali resistance, weather resistance, etc. at low temperatures on the outer surface of glass products, metal products, etc. in view of the above-mentioned problems.
There also hitherto existed the problem that when coloring coating operation of bottles is carried out under high-humidity environment in rainy weather, obtained colored bottles have haze.
Another object of the present invention is to provide colored coating compositions with which colored bottles having no haze can be obtained even if coating is carried out under the high-humidity environment.